Turbocharged engine systems may include a low-pressure EGR (LP EGR) system which recirculates exhaust gas from the exhaust passage downstream of a turbine to the intake passage upstream of a turbocharger compressor or a high-pressure (HP EGR) system which recirculates exhaust gas from the exhaust passage upstream of a turbine to the intake passage downstream of a turbocharger compressor. Alternatively, EGR may be implemented on a naturally aspirated engine where EGR is taken from the exhaust manifold and injected into the intake manifold. The recirculated exhaust gas may dilute the oxygen concentration of the intake air resulting in reduced combustion temperatures, and consequently, formation of nitrogen oxides in the exhaust may be reduced. LP or HP EGR systems may include an EGR cooler located in an EGR passage that couples an engine exhaust passage to the engine intake system. The EGR cooler may provide cooled EGR gas to the engine to further improve emissions and fuel economy. However, exhaust gas may contain soot, which may accumulate in the EGR cooler over a period of time. The accumulation of soot in the EGR cooler may cause EGR cooler fouling. Consequently, efficiency of EGR cooling may decrease resulting in degraded fuel economy and increased emissions. Further, due to accumulation of soot in the EGR cooler, there may be increased pressure drop across the EGR cooler, which may additionally affect fuel economy and emissions.
One example approach for determining EGR cooler degradation is provided by Freund et al. in US 2012/0096927 A1. Therein, a fouling layer in the EGR cooler is detected based on inlet and outlet pressure of the exhaust gas entering and exiting the EGR cooler, temperature of the exhaust gas exiting the EGR cooler, and inlet and outlet temperature of the EGR coolant entering and exiting the EGR cooler. In the illustrated approach by Freund et al., a detection system for determining EGR cooler fouling includes a first sensor for sensing an inlet pressure of the exhaust gas entering the cooler, and a second sensor for sensing exit pressure of the exhaust gas exiting the EGR cooler.
However, the inventors herein have identified issues with such an approach. For example, two additional sensors, one for sensing the inlet pressure of the exhaust gas entering the cooler and another for sensing the outlet pressure of the exhaust gas entering the cooler are required to determine a differential pressure across the EGR cooler. Further, additional electrical connections and control processes are required to transmit and process signals from the sensors. The additional sensors and connections lead to increased cost and size for implementation of the EGR cooler system.
Therefore, in one example, some of the above issues may be at least partially addressed by a method for an engine, comprising: determining degradation of an exhaust gas recirculation (EGR) cooler based on a change in a differential pressure across the EGR cooler greater than a threshold change, the differential pressure across the EGR cooler determined based on a differential pressure across an EGR valve located downstream of the EGR cooler and a pressure downstream of the EGR valve.
EGR systems employ a differential pressure over valve (DPOV) based measurement system to determine an EGR flow rate. The DPOV system may include a DPOV sensor to determine a differential pressure across an EGR valve located downstream of the EGR cooler. Further, an engine may include one or more EGR systems including one or more of a high pressure EGR (HP EGR) system, a low pressure EGR (LP EGR) system, or a naturally aspirated EGR system. In the LP EGR system, the pressure downstream of the LP EGR valve may be a compressor inlet pressure measured with a compressor inlet pressure (CIP) sensor. In the HP EGR system, the pressure downstream of the HP EGR valve may be an intake manifold pressure measured with an intake manifold pressure (MAP) sensor. The DPOV sensor may be utilized along with a CIP or MAP measurement (depending on the type of EGR system) to determine a differential pressure across the EGR cooler.
For example, when the EGR valve is closed, the differential pressure across the EGR cooler is zero. Therefore, a pressure upstream of the EGR cooler may be determined based on the DPOV sensor measurement and one of the CIP or MAP measurement when the EGR valve is closed. A pressure downstream of the EGR cooler may be determined based on the DPOV sensor measurement and the CIP or MAP when the EGR is flowing (that is, when EGR valve is not closed). Pressure loss or differential pressure across the EGR cooler may be determined based on the measured upstream pressure and the downstream pressure of the EGR cooler. The differential pressure may be calculated at different EGR flow conditions. The determined differential pressure across the EGR cooler may be utilized to determine a change in differential pressure across the EGR cooler compared to differential pressure across a new EGR cooler. EGR cooler fouling may be indicated if the change in differential pressure across the EGR cooler is greater than a threshold change.
In this way, by utilizing the existing DPOV measurement system for EGR cooler fouling determination, additional sensors and connections may not be required. Consequently, cost for implementing the detection system for EGR cooler fouling may be reduced.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.